The goal of this project is to define immune mechanisms and viral characteristics important in the pathogenesis of Aleutian disease (AD). Monoclonal antibodies were used to study antigenic differences between the ADV-G and Utah I ADV strains of ADV. Antibodies with reactivity for tissue derived Utah I ADV or tissue culture derived ADV-G were clearly delineated and new information was obtained regarding the specific antigenic determinants recognized by several mAbs whose precise reactivities were obscure earlier. Antibodies recognizing viral antigens purified from ADV infected cell cultures (ADV-G) recognize the major viral structural proteins of ADV while the viral associated antigen recognized by monoclonal antibodies reacting with tissue extracted ADV (Utah I) are low molecular weight proteins probably resulting from in vivo proteolysis of larger precursors. The affinities of the mAbs for virus strains were determined as well as the relative epitope densities recognized by individual mAbs. Recently developed mAb's against a Danish ADV strain, a Canadian ADV strain and two additional American strains are yet to be fully characterized but may provide specific markers for individual isolates and allow more precise information regarding the differing capacities of the individual strains to cause overt disease in mink.